The primary goal of the present research project is to conduct a prospective study of the characteristics of congenital esotropes. A sample of approximately 100 infants per year, referred to the Pediatric Ophthalmology clinic, will be followed longitudinally to assess the precursors, transient symptoms, and posttreatment characteristics of patients with intermittent and/or constant angles of eso-deviation. Referrals in the first postnatal year are of particular interest in that retrospective studies have provided conflicting evidence regarding the attainment of functional binocular vision (fusion and stereopsis) subsequent to surgical intervention. Each patient will receive the normal course of treatment established by the clinic staff seven years ago. Assessments of visual function will include four major methodological strategies. First, standard clinical examinations will be conducted both pre- and post-operatively, including consistent follow-up examinations at regular intervals. Second, a dynamic random-element stereopsis technique will be used to assess the presence or absence of global stereopsis during the post-operative period. Both preferential looking and EOG recordings to a stereoscopic OKN display will be used. Third, monocular VEP recordings will be gathered to assess the pre- and post-operative presence of amblyopia. Fourth, photographic measures of phorias, the AC/A ratio, and the resting positions of vergence and accommodation will be collected during the post-operative period. This prospective approach will enable us to validate the newly developed measures of stereopsis by correlating performance in pre-verbal infants and young children with subsequent performance on standard verbal measures. The assessments of visual functions related to fusion and stereopsis will enable us to evaluate the correlates of a loss in binocular function. Finally, the data base will allow us to evaluate two competing models of congenital esotropia, one based on peripheral aspects of visual function and the effects of early deprivation, and the other based on central neural anomalies due to genetic factors.